1. Field of the Invention
The present invention relates generally to techniques for handling fluid samples in chemical, biological, pharmacological and related processes. More particularly, it relates to spillproof microplate apparatus for receiving and securely holding fluid samples.
2. Description of the Prior Art
Multi-well microplates play an important role in conventional chemical, biological, pharmacological and related processes that are designed to analyze and/or synthesize large numbers of small fluid samples. Such conventional processes normally employ multi-well microplates as tools when processing, shipping and storing the small liquid samples. Many of these processes achieve high-throughputs by applying modern automation techniques, including robotics. In recent years, efforts have been directed at integrating the different prevailing microplate apparatus into the automation equipment of these high-throughput processes. Such integration efforts, however, have had only limited success. Specifically, spillage, leakage, evaporation loss, airborne contamination and inter-well cross contamination of liquid samples are some of the common deficiencies that limit the application of many standard microplate assemblies in high-throughput systems. Consequently, one of the most critical problems confronting designers of microplate apparatus has been finding techniques of preventing the loss and contamination of well contents without unduly complicating the structures and/or handling requirements of a microplate assembly.
A standard microplate assembly normally comprises a microplate having a plurality of open wells and a closure device for sealing the wells shut. Commonly available microplates generally embody a unitary molded structure comprising a rigid frame for housing a plurality of open wells arranged in a rectangular array. Standard well closures include resilient, press-fit stoppers, rigid screw caps, adhesive films and the like. Microplates come in a range of sizes; a well may be sized to hold as high as five milliliters or as low as only a few microliters of liquid. In addition, microplates come in a variety of materials, such as polystyrene, polycarbonate, polypropylene, Teflon, glass, ceramics and quartz. Conventional microplates found in many high-throughput systems comprise a 96-well geometry molded into an 8.times.12 rectangular array of open wells. Microplates with lower well densities (e.g., 24 and 48 wells) and higher well densities (e.g., 384 and 864 wells) are also available.
An important microplate application exists in high-throughput organic synthesis (HTOS) systems. HTOS has been rapidly gaining importance as a tool for the accelerated synthesis of small organic molecules. HTOS systems employ a variety of automation techniques, which significantly reduce the time required for the development of commercially acceptable compounds in the pharmaceutical, agrochemical and other specialty chemical industries. Most conventional HTOS systems simultaneously synthesize large groups of compounds while using standard microplate assemblies for the reaction, purification and shipment of such compounds. Another important microplate application exists in high-throughput screening (HTS) systems, which examine samples of pre-dissolved compounds for desired properties. HTS systems usually examine the samples while they are contained in the wells of conventional microplates. As such, automatic apparatus must manipulate conventional microplates and their contents during a typical HTS process. Consequently, a primarily requirement of a microplate assembly for use in HTOS and HTS systems is an ability to securely maintain a controlled environment for a liquid sample while the assembly is being manipulated in an automation process. In addition, a microplate assembly must provide means for adding reagents or other materials to an individual well or to multiple wells simultaneously. Further, a microplate assembly must allow for the mechanical mixing of well contents without risking spills, leaks or cross contamination.
Many HTOS systems deliver multiple samples as solutions of pre-dissolved compounds in microplate assemblies to various locations throughout the world. To prevent a loss of these solutions of pre-dissolved compounds from occurring during delivery, suppliers often convert the solutions into solids prior to shipment by freezing or other methods. Shipping compounds as solids rather than liquids, however, creates problems in dissolution that can complicate and inhibit subsequent sample evaluation procedures. Further, an unstable solid material may disperse on opening of a closed well prior to re-dissolution. Consequently, those skilled in the art have recognized that HTOS systems should preferably deliver solutions of compounds in their stable liquid form.
A need to deliver compounds as stable liquids creates handling and storage requirements that standard microplate apparatus cannot fully provide. As mentioned above, spills, leaks, sample evaporations and well contamination often limit the application of most standard microplate assemblies in high-throughput systems. A singular example involves the shipping of microplate assemblies in aircraft cargo hulls. At flying altitudes, a low ambient air pressure in an aircraft cargo hull may create a relatively large pressure difference across a well closure. Such pressure differences often cause press-fit closures to distort or even pop open, thereby permitting a resident liquid sample to spill, leak, evaporate, and/or cross contaminate other open wells. Similar problems also occur in conventional surface shipping because of mechanical shocks, vibrations and the like. Likewise, some chemical reactions create heat and pressure of sufficient magnitude in the confines of a sealed well such that the well closure will inadvertently open, thereby causing a resident sample to leak.
One attempt to resolve the shipping problems described above involves the use of a solution of a compound in an assay-compatible solvent that can be frozen, such as dimethyl sulfoxide. If the solution remains frozen, delivery may be achieved without spillage. This, unfortunately, is not always the case, since the useful life of cooling agents available for use in shipping environments rarely exceeds a few days. In addition, certain compounds will come out of solution on freezing and remain out on thawing, further complicating the use of cooling agents. Therefore, shipping techniques that involve cooling agents often create multiple sample-handling problems and require an inspection step prior to assay. Other attempts at solving these and similar problems have usually resulted in unduly complicating the structure of a microplate assembly while imposing elaborate and unacceptable requirements on automated processing systems.